The fundamental principles of fuel cell technology are well known in the art. A fuel cell generally comprises two electrodes sandwiched around an electrolyte.
In a typical fuel cell, the fuel is consumed at the anode and the oxidizer is consumed at the cathode. The cell operates as long as the fuel and oxidant are supplied. The hydrogen-oxygen fuel cell is the best known and most developed of the fuel cells. Oxygen passes over a cathode and hydrogen over an anode. The byproducts of the fuel cell are electricity, water and heat.
An advantage of fuel cells is that they produce electrical energy as long as fuel is supplied. Various types of fuel cells include phosphoric acid-based, proton exchange membrane, solid polymer, molten carbonate, solid oxide, alkaline, direct methanol, regenerative, zinc-air, and protonic ceramic. In an aluminum-air fuel cell, power is generated through an electrochemical reaction between the aluminum, once placed in an alkaline solution, and oxygen from the air. As the aluminum oxidizes in the alkaline solution, electricity is produced. The anode dissociation of aluminum occurs at the negative electrode according to the equations: Al+4OH−→AlO2−+2H2O+3e− and/or Al+4OH−→Al(OH)4−+3e−. The cathode reduction of the oxygen occurs at the positive electrode (gas diffusion cathode) according to the equation: O2+2H2O+4e−→4OH−.
While the aluminum-air fuel cell furthers the art in several areas, disadvantages still remain. The reaction of aluminum with water, acid or base releases hydrogen gas as a separate chemical reaction from the electrochemical reaction. In an aluminum-air galvanic cell, hydrogen production is problematic. Spent aluminum as aluminum hydroxide interferes with cell operation in an aluminum-air cell by formation of scale on cell components. Parasitic reactions of the aluminum with water drain the electrochemical energy from the cell when the cell is not in use. Once activated, the aluminum-air cell energy must be consumed until expended or it is lost by parasitic reactions.
Aluminum-air semi-fuel cells have an added disadvantage from the carbon dioxide in the air reacting with the hydroxide electrolyte in the cell to form carbonate. The carbonate limits the available hydroxide in the electrolyte.
Accordingly, what is needed in the art is a fuel cell that operates without a high pressure supply of hydrogen gas.
Another need in the art exists for a self-contained fuel cell that utilizes pure oxygen derived from chemical reaction rather than a highly pressurized source of air that contains carbon dioxide.
Another need in the art exists for a fuel cell that employs aluminum as a fuel energy source, but does not suffer from scaling or parasitic reactions.
Another need in the art exists for a light weight fuel cell energy supply that occupies a small volume.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed. However, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.